In mobile communication networks like GSM, UMTS or UMTS Long Term Evolution (LTE) networks, as illustrated on FIG. 1, a primary station 100 communicates with a plurality of secondary stations 110. These secondary stations 110 are typically handheld devices including batteries 111 supplying a communication device 112. To extend the operation time of the secondary stations without increasing the size of the batteries, it is currently desirable to reduce the power consumption of the secondary stations (or User Equipments (UEs)). In addition, if the battery charge becomes depleted, rather than exhaust the remaining energy, it would often be desirable to further reduce power and conserve energy, for example by adopting a more limited form of operation with reduced performance or fewer supported services.
It could be possible for example to transmit to the primary station a power limitation indicator, whose purpose is to allow the secondary station to indicate to the primary station and fixed network a condition of limited power availability. These indicators may be used to differentiate between devices that are mains-powered like secondary station 110b and those that are battery-powered or to indicate a low battery status.
When a secondary station registers for the first time (and on infrequent occasions thereafter), it indicates to the fixed network its capabilities via the UE Capabilities information elements or a UE category. This information could include, for example the number of UE Rx antennas and the maximum data rate that the UE can receive. The fixed network therefore has knowledge of what the UE is physically capable of doing and can instruct the UE to behave in accordance with network requirements and capacity, data delivery requirements and the UE's own operational limits.
It is to be noticed that it is difficult to define the threshold for signaling a change in status in a way that allows the primary station or fixed network to consistently respond in a meaningful way. For example, should the change in status be signaled at some predetermined battery capacity (e.g., 50% battery capacity? 20%? 10%?). A further associated consideration is that given that battery capacities vary according to the secondary station, such as, for example, battery size, technology and battery ageing and given that secondary station power consumption depends somewhat on implementation details, it would not be clear, for example, what “50% battery capacity” would actually mean for the secondary station. It is also not clear what it would mean for a user. For example, does the user expect to be able to place the secondary station on charge or does the user prefer to economize on energy consumption as much as possible?
In addition to limited battery power, the available signal processing power or signal reception capability of the secondary station may also depend on a host of other factors, which may include, the reception of MBMS (Multicast/Broadcast Multimedia Services, other transmissions, or processing the output of a video camera) are currently in use or not.